The monitor action queries the current status of a resource. It must discern between three different states:

foobar_monitor() {
    local rc

    # exit immediately if configuration is not valid
    foobar_validate_all || exit $?

    ocf_run frobnicate --test

    # This example assumes the following exit code convention
    # for frobnicate:
    # 0: running, and fully caught up with master
    # 1: gracefully stopped
    # any other: error
    case "$?" in
        0)
            rc=$OCF_SUCCESS
            ocf_log debug "Resource is running"
            ;;
        1)
            rc=$OCF_NOT_RUNNING
            ocf_log debug "Resource is not running"
            ;;
        *)
            ocf_log err "Resource has failed"
            exit $OCF_ERR_GENERIC
    esac

    return $rc
}

Stateful (master/slave) resource agents may use a more elaborate monitoring scheme where they can provide "hints" to the cluster manager identifying which instance is best suited to assume the Master role. Section 9.4, “Specifying a master preference” explains the details.

Note

The cluster manager may invoke the monitor action for a probe, which is a test whether the resource is currently running. Normally, the monitor operation would behave exactly the same during a probe and a "real" monitor action. If a specific resource does require special treatment for probes, however, the ocf_is_probe convenience function is available in the OCF shell functions library for that purpose.